590 Veterinary Medicine. , 



not common. At different points on Ivong Island, in New Jersey 

 and on the rich soils in the Mississippi valley and on the At- 

 lantic and Gulf coasts, osteoporosis often prevails enzootically 

 and has its recrudescences like rachitis. 



The process of rarefaction and softening may be thus stated. 

 In the Haversian canals and narrow spaces there is an active pro- 

 liferation of cells and increase of vascularity, with a gradual solu- 

 tion and removal, not only of the earthy salts, but also of the 

 fibrous matirix in the walls of these spaces. As in the normal 

 changes in bone, the absorption appears to be effected through 

 the large cells or osteoclasts grouped around the blood vessels. In 

 the osseous tissue, which abuts on the vascular tissue, are to be 

 found excavations, simple or irregular, (Howship's lacunae), 

 containing granular cells and the larger osteoclasts. In a similar 

 manner bone is softened and absorbed in connection with tubercle, 

 or the pressure of tumors, aneurisms, actinomycosis. In case of 

 recovery, repair takes place by the disposition of new bone, so 

 that the enlarged and rarefied bone may in the end become harder 

 than before. This applies especially to the cancellated bone. On 

 the articular ends of the affected bones, the granulation' tissue 

 makes its way into and through the cartilage of incrustation with 

 resulting active disease of the joint. 



The condition of the' bone is well illustrated in the dried or ma- 

 cerated specimen. Taken from a bad case in the active stage of 

 the disease, it crumbles under pressure and weighs as light as a 

 sponge, whilst from an advanced or recovered case, it is hard and 

 resistant, and weighs as much more than the normal bone as it 

 exceeds it in bulk. The morbid rarefaction usually affects the 

 whole skeleton more or less, yet in perhaps the majority of cases, 

 the change is greatest in the bones of the face, and the resulting 

 distortions are usually symmetrical on the two sides. It may 

 show mainly in the maxilla, which is thickened to twice or even 

 five times its normal thickness, it may show in rounded, general 

 swelling of the nasal and superior maxilliary bones and those 

 around the orbit, or it may involve the turbinated bones the 

 vomer and even the cartilaginous nasal septum. I^oosening and 

 evulsion of the molar teeth is common and snufiling breathing 

 may occur as in rachitis affecting the nasal bones of dogs and 

 swine. 



